Utils: Fix FilePath::isRootPath()

Change-Id: I287bae74469ba501ecb03d51f04f7aaa5f4a7268
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/filepath.cpp

@@ -204,7 +204,27 @@ FilePath FilePath::currentWorkingPath()
 
 bool FilePath::isRootPath() const
 {
-    // FIXME: Make host-independent
+    if (needsDevice()) {
+        QStringView path = pathView();
+        if (osType() != OsTypeWindows)
+            return path == QLatin1String("/");
+
+        // Remote windows paths look like this: "/c:/", so we remove the leading '/'
+        if (path.startsWith('/'))
+            path = path.mid(1);
+
+        if (path.length() > 3)
+            return false;
+
+        if (!startsWithDriveLetter())
+            return false;
+
+        if (path.length() == 3 && path[2] != QLatin1Char('/'))
+            return false;
+
+        return true;
+    }
+
     return *this == FilePath::fromString(QDir::rootPath());
 }
 
@@ -1346,15 +1366,15 @@ bool FilePath::contains(const QString &s) const
 
 /*!
     \brief Checks whether the FilePath starts with a drive letter.
-
-    Defaults to \c false if it is a non-Windows host or represents a path on device
-
     Returns whether FilePath starts with a drive letter
 */
 bool FilePath::startsWithDriveLetter() const
 {
-    const QStringView p = pathView();
-    return !needsDevice() && p.size() >= 2 && isWindowsDriveLetter(p[0]) && p.at(1) == ':';
+    QStringView p = pathView();
+    if (needsDevice() && !p.isEmpty())
+        p = p.mid(1);
+
+    return p.size() >= 2 && isWindowsDriveLetter(p[0]) && p.at(1) == ':';
 }
 
 /*!